I purchased this old truck from my Brother who used it to get back and forth to his first job before he took the plunge and took out a loan for a 3rd Gen with a hemi. He sold it to me for $800 with 319,000 miles on it.

Its primary issue at the time of purchase was a death wobble which turned out to be caused by a bad track bar joint. A local trade school teacher looked at it and suggested it would take 2 grand to fix the suspension, $50 later at a junkyard and it's fixed... idiot. But I digress.

The other problem was a stalling issue. It was rather insignificant when I first got the truck but has slowly progressed to be worse over time until now it's a common, intermittent, "stalls, cranks, doesn't start back up" sort of issue, making it too unreliable to be my daily which I feverishly miss having it as.

Normally the truck drives fine. It will start, shift, drive just fine and get me from A to B for about 20-50 miles. I can puttz around and run errands with it until "it" happens.... I come to an intersection and it either stalls on the spot at the stop sign or runs like total **** out of nowhere, rough idling, wanting to stall when I give it throttle, etc., as well as a hissing noise that sounds like a vacuum leak, most prominent at low throttle, that also appears and disappears with the problem. (intermittent vacuum leak? strange...)

Usually I end up stranded for about 10-20 minutes when this happens. I have an inductive spark timing light that I used to determine that I AM indeed getting spark. Fuel pump is new, and I am getting pressure. fuel injectors were given a rough cleaning about a year ago, but have not checked for pulses when this issue comes up. The only sure indicator I have involves the fuel pump relay.

I've noticed that when it stalls, I can immediately crank the engine, but the engine will only crank, showing almost no signs of turning over, UNTIL I disconnect the fuel pump relay. As soon as I do this, I can crank the engine and get some sort of sputter if not a full restart almost as soon as I crank the engine. Yes, it only starts back up when the relay is UNPLUGGED.

If and when it does start up running on residual fuel pressure, often I can run around back to the fuse box and plug the relay back in, in which case the engine usually dies IMMEDIATELY upon reconnection of the relay.

In an attempt to diagnose the fuel system's electrical, I installed a home brew light/switch box wired from the under hood fuse box to the cab, with lights that indicate the presence of voltage on each side of the relay, as well as a switch that allows me to manually apply voltage to the fuel pump. This little device comes in handy when it comes to playing the game of cat and mouse that ensues as I stall, disconnect the relay, start it, and attempt to plug the relay back in WITHOUT killing the RPMs.

Once I win, upon reconnecting the relay the truck will finally sputter a bit and then go back up to normal RPM, normal throttle response, normal everything, and will continue running normally for 20 minutes, two weeks, who knows....

I suspect that there may be an issue with the ECM? I have a random assortment of codes, none of which pertain directly to the symptoms; IAC, coolant temp, ignition coil, etc., all of which are new or functional. But this seems like very specific behavior pertaining to the relay trick I learned... any thoughts?

 

Coolant Temp........ That one is mighty suspicious. If you have an intermittent failure of the temp sensor, the PCM thinks that engine temp is -40*, and positively DUMPS fuel.... Removing the fuel pump relay lets the engine clear the flood, and the truck will once again start and run. (until either the fuel is all gone, or, you plug the relay in, and it once again floods out.)

Given that your truck is a 97, you have two temp sensors on the engine, a two-wire, just to the drivers side of the thermostat housing, the the PCM pays attention to, and a one wire on the passenger side of the intake, right behind the alternator, that is for the gauge in the dash.

Which one did you replace?

 

That was my suspicion when I first encountered the issue and whipped out my OBD-II scanner. That was the only code I had come across so far, except wondered if perhaps the computer should acknowledge that there was an issue and thus prevent fuel enrichment from taking place based on coolant temperature readings. Obviously if there's a code the computer should recognize an issue, you would think.

But I was not aware there were two temp units, both an ECU and Dash sending sensor... I was under the impression that there was only one sensor and, depending on the individual vehicle, the sensor either sent its info to both the ECU *AND* the dash, or the dash gauge was informed by the ECU. When I purchased the replacement part it was noted that the difference included one sensor type having 2 electronic connection prongs and the other having only 1 (grounded through the block?).

If memory serves, I replaced the unit adjacent to the thermostat housing with the type of sensor that only has one connection. I do indeed get temperature readings on the dashboard temp gauge after warm up (when the engine is running normally, unsure if when not) and also at the ECM, judging by a "snapshot" I took of the OBD-II live data feed when the engine was running properly between its tantrums, at 70F shortly after startup on a cold Michigan day.

 

Whereabouts in Michigan?

I am actually surprised it will even run that way. Verify your sensors. Dodge did some odd and strange things over the years, and swapping around sensor locations isn't out of the realm of possibility.

 

Surprised that it will run what way?

I will have to refer to the repair manual if I can find it to see if I can track down where I was informed of the difference between the one- and two- lead sensors. The Haynes manual I have is good at recognizing differences over the years in these Gen-II's, if I can just find the bloody thing.

Oh, and in Bay City MI, right in the webbing of the thumb if you catch the reference.

 

Yep. I know where that's at. Haven't been up that way in a while though. (I don't get out much. )

If the sensor next to the thermostat housing is supposed to be a two wire, and you have a one wire sensor in there, the PCM shouldn't be getting any indication of engine temp there. (and it should set a code.) Not sure what the PCM would do in such a case.... It *might* default to the -40 degrees, in which case, your engine would run incredibly rich. (if it ran at all...)

You can download a factory service manual for your truck from here.

 

If I remember correctly the plug on the wiring harness also only had on electrical lead. As I said the ECU and dash gauge are both functional as far as I know. My main purpose for mentioning these random codes has more to do with the ECM itself. I've heard that bad ECU's can sometimes throw up a collection of persistent codes that are nonsensical, intermittently triggered, etc.

 

Still, think I would take a look at both of those sensors, and their connectors. One of them should be a one-wire, and the other should be a two-wire. I don't see dodge making that kind of dramatic change mid-model year.

The reason I am so stuck on these, is it would explain your symptoms rather well..... If this ain't it, we can move on to something else.

 

Update: had to leave the truck's battery on a trickle charger the last couple days, so when I went to go reinstall the battery today I decided to take advantage of the strangely good weather here in Bay City and start it up.

After it was running I putzed around swinging a wrench at the ECM to see if I could trigger anything, wiggled wires, etc. Nothing happened until after a few minutes the truck's idle shot up to about 1100 RPM judging by the sound. I ran around to stab the throttle a few times and that was it, it stalled, wouldn't start with the relay in, etc... I made a mad dash for my OBD-II scanner.

After getting the truck going lacking-fuel-relay, the live data on the scanner showed -40C for coolant temp. I ran to get the other of my two name-brand repair manuals, I found a distinction between the Engine Coolant Temp sensor and the dash gauge sending unit. You were indeed correct HeyYou.

I found the other sensor, the two-wire one just behind the A/C compressor that apparently goes to the ECM. Here's the strange part: The sensor was completely snapped in half, with one half connected to the wiring harness looking like a rusted thermocouple just flapping in the breeze, and the other half screwed in to the block looking like little more than a bolt with some corrosion on it. Strange considering the issue was rather intermittent, as I don't suppose the right speed bump would magically flop the sensor bits back together to function.. this sensor was obviously and completely inoperable.

21 bucks at O'Reilly auto parts later I have seemingly reliable coolant temp data to the ECM. I have not driven the truck anywhere yet (worst case scenario, being stranded in 15 degree weather isn't fun). However it did stay running in the drive way for the better part of an hour and a half or two while I cleaned the truck out and addressed some other zip-tie-and-duct-tape issues.

Idle stayed at a steady 600 RPM, and with occasional stabs at the throttle giving no hesitation or sputter except for an uncomfortable dip down to about 350-400 RPM before returning to Idle.

I cleared the codes just after the sensor replacement and the only other code to come up was a "lean mix - bank limit". Perhaps a good thing in light of our theories?

Regardless I'm still skeptical of future test drives considering the nature of the condition I found the sensor in, as I mentioned earlier.

 

Wonder if you have more than one issue......

For the low idle, it might just be the PCM hasn't learned the engine again yet, or, you might need to clean the throttle body.... Cleaning it sure wouldn't hurt. Pay special attention to the IAC well.

Aside from that, I am thinkin' you got it licked.